Solvent dewaxing



Unite rates This invention relates to an improved method for effectingthe removal of Wax from waxy materials. More particularly, thisinvention relates to the solvent dewaxing of waxy materials, such as aWaxy petroleum fraction. In accordance with one embodiment thisinvention is related to the solvent dewaxing or fractionalcrystallization of mixtures such as mixtures of fatty acids, vegetableoils, animal oils and fats, fish oils and the like.

In the solvent dewaxing of waxy materials such as mineral oils it is thepractice to admix the waxy material to be dewaxed with a liquid dewaxingsolvent and to cool the resulting admixture to a suitable low dewaxingtemperature to precipitate substantially all of the waxy material. Theresulting precipitated wax is then removed by filtration from theresulting dewaxed oil.

In many dewaxing plants the filtration step wherein the precipitated Waxis separated from the dewaxed oil, is the critical operational step inthe sense that the filtration operation is the limiting factor withrespect to the capacity of the dewaxing plant. In many instances if therate of filtration of the precipitated Wax from the dewaxed oil isincreased the plant capacity for the production of dewaxed oil can beproportionally increased.

Accordingly it is an object of this invention to provide an improveddewaxing process.

Another object of this invention is to provide an improved process forthe solvent dewaxing of waxy mineral oils.

Still another object of this invention is to provide a method forincreasing the dewaxing capacity of a dewaxing plant such as a plant forthe dewaxing of waxy mineral oils, or a plant for the solvent fractionalcrystallization of fatty acids and/or their glycerides, such asvegetable oils, e.g. tung oil, soy bean oil, perilla oil, cotton seedoil, linseed oil, animal oils and fats such as lard, sperm oil, etc. andfish oils such as cod fish oil, herring oil, sardine oil, etc.

Yet another object of this invention is to provide a method forcontrolling the number and size of crystals such as wax crystals in asolvent dewaxing operation.

How these and other objects of this invention are accomplished willbecome apparent in the light of the accompanying disclosure. In at leastone embodiment of the practice of this invention at least one of theforegoing objects will be achieved.

In accordance with this invention it has now been discovered that animproved solvent dewaxing or solvent fractional crystallizationoperation is obtained by shock chilling the waxy oil or mixture to bedewaxed or fractionated from a temperature just above the cloud point orinitial haze temperature, to a temperature in the range -50 degreesFahrenheit below said cloud point. Following the shock chillingoperation the resulting chilled admixture is then cooled in the usualmanner to the final dewaxing or crystallization temperature at whichtemperature the resulting precipitated solids, waxy material and thelike, are removed by filtration.

More particularly, in accordance with this invention it has beendiscovered that an improved dewaxing operation is provided when a liquidWaxy mixture, such as a waxy mineral oil, is cooled in the substantialabsence of dewaxing solvent to a temperature at or just above the cloudpoint of said waxy mineral oil. The resulting cooled waxy oil is thenshock chilled by directly admixatent ing therewith cold dewaxingsolvent. The amount and/ or temperature of the cold dewaxing solventwhich is directly admixed with the waxy oil during the shock chillingoperation is such that the waxy oil in the resulting admixture of oiland dewaxing solvent is substantially instantaneously chilled from atemperature at or slightly above the cloud point of the oil to atemperature in the range 10 to 50 degrees Fahrenheit below said cloudpoint. The resulting chilled admixture is then gradually cooled,preferably in the presence of additional dewaxing solvent, to the usualdewaxing temperature, such as a temperature in the range 20 F. to -4-0F., more or less, and the resulting precipitated Wax separated byfiltration.

Explanatory of the practice of this invention it is speculated that byshock chilling the waxy material undergoing dewaxing or fractionation,thereby subjecting the waxy material to a rapid initial chilling througha definite temperature range, control of the type of wax crystal formedas a result of this shock chilling is effected. It is also speculatedthat the number of wax crystals formed during this shock chillingoperation is also controlled depending upon the extent of shockchilling, i.e. how far below the cloud point the temperature of theresulting admixture is after shock chilling. Accordingly, it isspeculated, after the initial shock chilling has established the numberand characteristic or type of wax crystals, the cooling of the resultingadmixture comprising precipitated wax, waxy oil and dewaxing solvent canbe continued in a normal and conventional manner to permit increasingthe size of the individual wax crystals, already started or producedduring the wax chilling operation without substantially increasing thenumber of Wax crystals. More particularly, it is speculated that thissubsequent cooling operation can be carried out at a rate low enough andadjusted to permit wax to accumulate on or to crystallize on theinitially-formed wax crystals rather than to form new, smaller crystalsas this subsequent cooling operation with consequent wax crystalformation or wax removal is continued.

As indicated, the practice of this invention is generally applicable tothe dewaxing of mineral oils, such as waxy residual petroleum fractionsor waxy distillate petroleum fractions. The practice of this inventionis also applicable to the fractionation, by solvent fractionalcrystallization, of animal or vegetable fats or oils, wherein a fractionthereof is precipitated by cooling in the presence of a solvent and theresulting precipitated fraction separated by filtration.

The practice of this invention is generally applicable to any solventdewaxing operation such as a propane dewaxing operation or the wellknown solvent dewaxing operation employing as the dewaxing solvent amixture of a mineral oil solvent such as an aromatic hydrocarbon, e.g.benzene, toluene and the like, and a wax anti-solvent such as a normallyliquid aliphatic ketone containing from 3 to 9 carbon atoms permolecule, e.g. acetone, methyl ethyl ketone, methyl isobutyl ketone,methyl n-propyl ketone and the like. In this type of solvent dewaxingthe dewaxing solvent would comprise a suitable aliphatic ketone and anormally liquid aromatic hydrocarbon in an amount in the range 20-80%and 20% by vol., respectively.

In the practice of this invention the material undergoing dewaxing orsolvent fractional crystallization, just prior to shock chilling, is ata temperature at or just above the cloud point or initial hazetemperature of said mixture, such as a temperature in the range 0-10degrees Fahrenheit above said cloud point. By cloud point or initialhaze temperature is meant that temperature at which crystals orprecipitated solid material first begin to appear and to be observed, asby the observation of a haze therein, in the mixture to be fractionatedin the substantial absence of a solvent.

In the shock chilling step in the practice of this invention thetemperature of the resulting admixture, waxy mixture and dewaxingsolvent, after shock chilling is in the range 10-50 degrees Fahrenheitbelow the cloud point of the waxy material undergoing dewaxing. Theshock chilling of the waxy mixture is carried out under conditions suchthat the temperature of the waxy material is substantiallyinstantaneously reduced from a value at or just above the cloud point toa value in the range 10-50 degrees Fahrenheit below the cloud point.This is achieved in the practice of this invention by directlyintroducing into contact with the waxy mixture an amount of colddewaxing solvent. The temperature of the dewaxing solvent and the amountof dewaxing solvent with respect to the waxy material to be shockchilled is adjusted so that substantially instantaneous cooling orchilling of the waxy material through or from the cloud point thereof toa temperature 10-50 degrees Fahrenheit and below is eifected. It ispointed out that the lower the temperature of the dewaxing solventemployed in the shock chilling operation the less the amount of dewaxingsolvent required to efiect the desired shock chilling. This initialshock chilling of a given portion of the waxy mixture undergoingdewaxing is effected substantially simultaneously upon admixture of thecold solvent, or within a relatively very short time, dependent upon thetime required to effect substantially complete admixture of the colddewaxing solvent with the waxy mixture undergoing dewaxing, certainlynot longer than about 30 to 60 seconds and usually in the range 5-20seconds, more or less.

Following the shock chilling operation the resulting chilled admixtureof waxy material, now containing some solids or solid waxy materialprecipitated therein, is gradually cooled in the conventional manner andin the presence of additional solvent, if sufficient solvent has notalready been added during the shock chilling operation, to the finaldewaxing temperature. This cooling of the waxy mixture together withdewaxing solvent, subsequent to the shock chilling operation, is carriedout at a normal rate, such as a cooling rate in the range 0.3-3.0degrees Fahrenheit, more or less, per minute. Upon reaching the finaldewaxing temperature, such as a temperature in the range 20 F. to 40 F.,the resulting admixture of precipitated wax, dewaxing solvent anddewaxed oil is subjected to filtration, preferably by means of a vacuumrotary filter wherein the admixture of oil, dewaxing solvent and solidwax is drawn through a filter medium, the solid wax being retained onthe filter medium, washed, dried and removed in a continuous manner.

The following tests are illustrative of the practice of this invention.

In test No. 1 portions of a waxy petroleum distillate fraction having acloud point or initial wax haze temperature of about 50 F. were cooledfrom about 60 F. to about 52 F., about the cloud point of 50 F. in thesubstantial absence of dewaxing solvent. The cooled oil was thensubjected to shock chilling by directly admixing therewith 0.5 part byvolume, based on the oil, of dewaxing solvent having the composition 55%vol. methyl ethyl ketone and 45% vol. toluene. The dewaxing solventprior to admixture with the waxy oil was at a temperature of 18 F. As aresult of shock chilling the waxy oil by directly admixing therewith thecold dewaxing solvent the temperature of the admixture was 36 F., atemperature decrease of about 14 degrees Fahrenheit with respect to theinitial temperature of the waxy oil. Following the shock chillingoperation the resulting admixture was then cooled from 30 F. to 6 F. ata rate of about 1.2 degrees Fahrenheit per minute. During thissubsequent cooling operation there was added to the cooled admixture 0.1part by volume, based on the oil, of additional cold dewaxing solvent ata temperature of 0 F. This additional dewaxing solvent was added to thecooled admixture at an admixture temperature of about 0 F. Followingthis operation the resulting precipitated wax was removed from thedewaxed oil-solvent admixture at a temperature of 6 F. by means of arotary filter. During the wax filtration operation the rate offiltration of the admixture was observed.

In another test, test No. 2, portions of the same waxy distillate oilhaving a cloud point of about 50 F. were cooled to this temperature. Atthis temperature there was directly admixed with the cooled oil 0.2 partby volume, based on the oil, dewaxing solvent at a temperature of 50 F.,substantially the same temperature as the oil. It was observed that thetemperature of the resulting admixture of oil and dewaxing solvent was46 F. sub stantially immediately after the addition of the dewaxingsolvent to the oil. This reduction in temperature was attributed to thenegative heat of solution of the dewaxing solvent in the oil. Followingthe admixing of the dewaxing solvent with the oil the resultingadmixture was cooled from 46 F. at a rate l.1 F. per minute over thetemperature range 46 F. to 5 F. During this cooling period 0.3 part byvol. additional solvent was added to the oil-solvent admixture at anadmixture temperature of 35 F. and 0.5 part by vol. solvent added to theadmixture at the admixture temperature of 0 F. When the resultingadmixture of precipitated wax, dewaxed oil and dewaxing solvent reachedthe temperature of 5 F. the precipitated wax was separated therefrom bymeans of a rotary filter. The rate of filtration during this operationwas observed.

In another test, test No. 3, portions of a waxy distillate oil having acloud point of about 63.5 F. at a temperature F. were admixed with 0.9part per volume, based on the oil, of dewaxing solvent. The resultingadmixture was then cooled at a rate of about 1.0 degree Fahrenheit perminute from -a temperature of about 120 to 46 F., the cooling rate wasthen reduced to 0.7 degree Fahrenheit per minute. When the resultingcooled admixture reached a temperature of 6 F. there was added thereto0.4 part per volume, based on the oil, of additional dewaxing solvent ata temperature of 6 F. The resulting admixture was then cooled to -10 F.Following this cooling operation/the admixture containing theprecipitated wax, dewaxed oil and dewaxing solvent was then subjected tofiltration by means of a rotary filter. During this filtration operationthe rate of filtration of the admixture was observed.

The results of these tests with respect to filtration rates are setforth in accompanying Table I.

TABLE I Filter Production Rates in gals per hr. of Dewaxed Oil per sq.ft. of filter surface 1 For Dewaxed Oil Yield and v0]. percent of chargeTest No. 1: Shock chilling from about 2 F. above initial hazetemperature 5. 8 8. 2' Test N o. 2: Shock chilling from 2 F. belowinitial haze temperature 4. 7 5. 8 Test No. 3: Normal solvent dewaxingand cooling. 3. 8 5. 3

substantially improved, thereby potentially increasing the capacity of adewaxing plant, particularly those plants where the wax removal or waxfiltration step is the limiting operation with respect to dewaxing plantcapacity. It is to be noted that the benefits of the practice of thisinvention are obtainable independent of the yield of dewaxed oil, i.e.the wax filtration rate increased whether or not the yield of dewaxedoil was increased, the yield of dewaxed oil being dependent upon thedewaxing temperature employed and the severity of wax cake washing.

In the practice of this invention various ratios of solvent, such asdewaxing solvent, to the mixture, such as waxy oil mixture, to befractionated or dewaxed may be employed depending upon the character ofthe mixture to be fractionated and/or the amount of wax or componenttherein to be separated and/or the character of said component and/ orthe extent of removal of said component desired. Usually a solvent tocharge mixture ratio in the range 0.3-10.0, more frequently in the range1.0-5.0, gives satisfactory results.

As will be apparent to those skilled in the art many modifications,changes and substitutions may be made in the practice of this inventionwithout departing from the spirit or scope thereof.

I claim:

1. A method of solvent dewaxing a waxy petroleum fraction whichcomprises cooling a waxy petroleum fraction in the substantial absenceof dewaxing solvent to a temperature in the range to degrees Fahrenheitabove the cloud point of said petroleum fraction, shock chilling theresulting cooled petroleum fraction by ad mixing therewith cold dewaxingsolvent effecting substantially instantaneous cooling of the resultingmixture to a temperature in the range 10-50 degrees Fahrenheit below thecloud point of said petroleum fraction, and subsequently cooling theresulting admixture to dewaxing temperature and separating by filtrationthe resulting precipitated wax from said admixture.

2. A method in accordance with claim 1 wherein said dewaxing solventcomprises a liquid admixture of methyl ethyl ketone and toluene.

3. A method in accordance with claim 1 wherein the cloud point of thewaxy petroleum fraction is in the range 40-140 F.

4. A method in accordance with claim 1 wherein said waxy petroleumfraction is cooled to a temperature about 2 degrees Fahrenheit above thecloud point prior to shock chilling by contact with cold dewaxingsolvent.

5. A method of dewaxing a waxy petroleum fraction which comprisescooling said waxy petroleum fraction in the substantial absence ofdewaxing solvent to a temperature just above the cloud point or initialwax haze temperature of said waxy petroleum fraction, shock chilling thecooled waxy petroleum fraction substantially instantaneously to atemperature in the range 10-50 degrees Fahrenheit below said cloud pointby directly admixing with said cooled waxy petroleum fraction colddewaxing solvent, cooling the resulting admixture of waxy petroleumfraction and dewaxing solvent in the presence of additional dewaxingsolvent to a temperature in the range 15 F. to 20 F. and separating byfiltration the resulting precipitated wax.

6. A method in accordance with claim 5 wherein said dewaxing solventcomprises an aliphatic ketone having from 3 to 9 carbon atoms permolecule and a normally liquid aromatic hydrocarbon.

7. A method in accordance with claim 6 wherein said dewaxing solventcomprises an aliphatic ketone having from 3 to 9 carbon atoms permolecule and said aromatic hydrocarbon in an amount in the range 20-80%and 20% by vol., respectively.

8. A method in accordance with claim 5 wherein said dewaxing solventcomprises methyl ethyl ketone and toluene in an amount in the range20-80% and 80-20% by volume, respectively.

9. A method in accordance with claim 5 wherein said waxy petroleumfraction is shock chilled by contact with cold dewaxing solvent to atemperature in the range 10-20 degrees Fahrenheit below said cloudpoint.

References Cited in the file of this patent UNITED STATES PATENTS1,974,398 Ellsberg Sept. 18, 1934 2,098,007 Mapes et al Nov. 2, 19372,303,703 Miller Dec. 1, 1942 2,614,065 Wanderer et al. Oct. 14, 19522,760,904 Ford Aug. 28, 1956 2,880,159 Livingstone et al Mar. 31, 1959

1. A METHOD OF SOLVENT DEWAXING A WAXY PETROLEUM FRACTION WHICHCOMPRISES COOLING A WAXY PETROLEUM FRACTION IN THE SUBSTANTIAL ABSENCEOF DEWAXING SOLVENT TO A TEMPERATURE IN THE RANGE 0 TO 10 DEGREESFAHRENHEIT ABOVE THE CLOUD POINT OF SAID PETROLEUM FRACTION, SHOCKCHILLING THE RESULTING COOLED PETROLEUM FRACTION BY ADMIXING THEREWITHCOLD DEWAXING SOLVENT EFFECTING SUBSTANTIALLY INSTANTANEOUS COOLING OFTHE RESULTING MIXTURE TO A TEMPERATURE IN THE RANGE 10-50 DEGREESFAHRENHEIT BELOW THE POINT OF SAID PETROLEUM FRACTION, AND SUBSEQUENTLYCOOLING THE RESULTING ADMIXTURE TO A DEWAXING TEMPERATURE AND SEPARATINGBY FILTRATION THE RESULTING PRECIPITATED WAX FROM SAID ADMIXTURE.